Electronic devices, such as computer systems or wireless cellular telephones or other data processing systems, may often include a display or display device, such as a liquid crystal display (LCD) or light emitting diode (LED) display, for providing a user interface with various images, programs, menus, documents, and other types of information. The display may illuminate or display various colors with a color space such as the CIE XYZ color space created by the International Commission on Illumination in 1931. A specific method for associating three numbers (or tristimulus values) with each color is called a color space. The human eye has receptors for short, middle, and long wavelengths, also know as blue, green, and red receptors. The CIE XYZ color space includes a set of tristimulus values called X, Y, and Z which are also roughly red, green, and blue, respectively.
The concept of color includes brightness and chromaticity. For example, the color white is a bright color while the color grey is considered to be a less bright version of that same white color. In other words, the chromaticity of white and grey are the same while their brightness differs. The CIE XYZ color space was deliberately designed so that the Y parameter was a measure of the brightness or luminance of a color. The chromaticity of a color was then specified by the two derived parameters x and y, which are functions of all three tristimulus values X, Y, and Z. FIG. 1 illustrates a CIE (1931) xy chromaticity diagram with all of the chromaticities visible to the average person. This region is called the gamut of human vision. The gamut of all visible chromaticities on the CIE plot is the tongue-shaped or horseshoe-shaped object. The curved edge of the gamut is called the spectral locus and corresponds to monochromatic light.
The color temperature of a light source is determined by comparing its hue with a theoretical, heated black-body radiator. Hue is that aspect of a color described with names such as “red”, “yellow”, etc. The Kelvin temperature at which the heated black-body radiator matches the hue of the light source is that source's color temperature. An incandescent light is very close to being a black-body radiator. However, many other light sources, such as fluorescent lamps, do not emit radiation in the form of a black-body curve, and are assigned what is known as a correlated color temperature (CCT), which is the color temperature of a black body which most closely matches the lamp's perceived color. Some common examples of color temperatures include a 2800 K Tungsten lamp (incandescent lightbulb), a 4100 K Moonlight, a 5000 K Daylight (D50), 6500 K Daylight (D65), and a 9300 K TV screen (analog). FIG. 1 also illustrates a black body locus or white point locus, with color temperatures indicated. The lines crossing the black body locus are lines of constant correlated color temperature.
The display of an electronic device may need to be calibrated in order to better match colors between the display and other types of media including other displays, paper sources, etc. One prior system with multiple displays includes an operating system and frame buffers for each display. Each frame buffer uses a color profile associated with the corresponding display that it drives; this can be referred to as “non-mirrored mode.” For example, a first color profile and first look-up table (LUT) can be associated with a first display and a second different color profile and second different LUT can be associated with a second display. This provides independent color management per each display. Display data is buffered in window buffers and then transferred to frame buffers to display the corresponding media on the displays.
Another prior system can use two displays to show the same image; this can be referred to as “mirrored mode.” In this case, the display is driven with display data that is processed with a single color profile designed for one of the two displays. However, the displays may have different color gamuts. The system performs color management for one of the displays with one color profile and the display data to be displayed is mirrored onto both displays. In this case, since color management is performed for only one of the displays, the color presented on one display differs from the color presented on the other display.